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Friday, January 6, 2017

Lucy and Psyche Asteroid Missions

Earlier this week, Santa in the guise of NASA managers brought the
solar system small bodies science community a sack full of belated Christmas
presents.The Venus science community
was unfortunately left with no presents under the tree.

An artist’s conception of the Lucy
spacecraft flying by the Trojan Eurybates and the Psyche spacecraft in orbit
around asteroid 16 Psyche.Credit: SwRI
and SSL/Peter Rubin

The losers were a Venus mapping mission and Venus atmospheric probe
mission.Their rejection will continue a
drought in NASA launches to our sister world that followed the Magellan
mission’s launch in 1989.When asked why
neither Venus mission was selected, the head of NASA Planetary Science
division, Jim Green, answered that the competition for selection was among
mission proposals and not between destinations.He said that the review teams found that the proposals for the Venus
missions scored less well than the proposals for the selected missions.

Dates for key events in the Lucy and Psyche missions.

Lucy Mission

Encounter date

Location

Dia-meter (km)

Spectral type

Launch

Oct. 2021

DonaldJohanson

April 2025

Main belt

3.9

C

Eurybates

Aug. 2027

Greeks

64

C

Polymele

Sept. 2027

Greeks

21

P

Leucus

April 2028

Greeks

34

D

Orus

Nov. 2028

Greeks

51

D

Patroclus/Menoetius

March 2033

Trojans

113/ 104

P

Psyche Mission

Launch

Oct. 2023

16 Psyche

2030

Main belt

210

M

The Lucy mission, named after the famous humanoid fossil, will survey
two asteroid fossil beds for clues to the early history of the solar system.It will study the Trojan asteroids that share
Jupiter’s orbit, either preceding (the “Greek” camp in L4 Lagrangian orbits) or
trailing (the “Trojan” camp in L5 Lagrangian orbits) the giant planet.Telescope observations suggest these bodies
have primitive compositions, several of which don’t appear to be represented in
our meteorite collections and that haven’t yet been visited by spacecraft.

The planned orbits and asteroid encounters for the Lucy mission.Credit: SwRI

The origin of these asteroid populations is a mystery, and its solution
would tell scientists much about the dynamics of the young solar system.Planetary scientists now believe that the
orbits of the giant planets migrated in toward the sun and then out again soon
after their formation.In the process,
they scattered asteroids and comets hither and thither.Jupiter’s Lagrangian orbits may have been sticky
gravitational traps that caught a diverse sample of bodies that originated from
throughout the outer solar system to its fringes.Another theory suggests that the Trojans
originated in the same region as Jupiter and followed it in its movements and
are therefore samples of conditions where Jupiter formed.Either way – and it’s possible that the present
population represents a mixture of sources – these bodies hold clues to
conditions and processes from the infancy of our solar system.

The most recent planetary decadal survey emphasized the importance of these
bodies by prioritizing a mission to explore them.“Trojan asteroids, at the boundary between
the inner and outer solar system, are one of the keys to understanding solar
system formation.Originally thought to
have been captured from the outer parts of the asteroid belt, Trojan asteroids
are proposed in new theories to have been captured instead from the Kuiper belt
during a phase of extreme mixing of the small bodies of the solar system.In-depth study of these objects will provide
the opportunity to understand the degree of mixing in the solar system and to
determine the composition and physical characteristics of bodies that are among
the most primitive in the solar system.”

The report listed three key questions related to the study of Trojan
asteroids in context with other bodies throughout the outer solar system:

What were the initial stages, conditions, and
processes of solar system formation and the nature of the interstellar matter
that was incorporated? Important objects for study: comets, asteroids, Trojans,
and Kuiper belt objects.

“What governed the accretion, supply of water,
chemistry, and internal differentiation of the inner planets and the evolution
of their atmospheres, and what roles did bombardment by large projectiles play?
Important objects for study: Mars, the Moon, Trojans, Venus, asteroids, and
comets.

The Lucy looks to the New Horizon Pluto mission for two of its
instruments with near copies of that mission’s LORRI high resolution camera and
the RALPH color camera and imaging spectrometer.The
third instrument is a thermal emission spectrometer derived from an instrument
on the OSIRIX-REx asteroid mission.Data
from these instruments will provide information on the processes that shaped
these worlds, their composition, and physical properties of the surface
material such as the average size of particles.Tracking of the spacecraft’s radio signal will provide information on
each asteroids mass and therefore density which provides clues to their
composition and to whether they are solid objects or rubble piles.

The creativity behind the Lucy mission is that its proposers found a trajectory
that over 12 years encounters seven asteroids (two in a binary system).The Lucy mission will encounter its targets
using two large solar orbits that take it out to the orbit of Jupiter to
encounter the Trojan swarms.In the
first of these orbits, it will fly by a tiny main belt asteroid (DonaldJohanson,
named after the paleontologist who led the team that found the Lucy fossil) and
then four diverse asteroids in the Greek population. The next orbit takes it into the Trojan
population for a single encounter with a binary asteroid system whose
characteristics are similar to those of comets suggesting they may be refugees
from the distant outer solar system.After this second long orbit, the spacecraft should have sufficient fuel
for further encounters with main belt and Trojan asteroids in a third orbit if
NASA approves funding for an extended mission.(Each of these extended orbits appear to take approximately six years,
so any encounters from an extended mission seem likely to occur in the late
2030s.)

The Lucy mission will study a variety of asteroids through brief, but
intense flybys.It will be something
like photographing boulders along the roadside while speeding by on a freeway
for later analysis.The second Discovery
mission selected, by comparison, will be like parking your car next to one
especially intriguing boulder for a nearly yearlong examination.

The single destination for the Psyche spacecraft will be the relatively
large asteroid of the same name.This
world is the largest of the rare (type M) metallic asteroids.Psyche could be unique remnant of a class of
asteroids that formed so close to the sun that only metals could condense out
of the early solar nebula and was later flung into the main belt of the
asteroids.Or it could be the inner,
metallic core of a once larger protoplanet that had its overlying layers of
rock and possibly ice blasted off by impacts with other asteroids.

Telescopic observations reveal that Psyche’s surface is 90% metallic
and 10% silicate rock. The spacecraft’s instruments should distinguish
between these scenarios by measuring the composition in detail and looking at
the arrangement of the silicate material. The mission’s principal
investigator wrote me, “If the silicate material is primarily high-magnesian
pyroxene or olivine, then these silicates are likely the remnants of a
crystallizing magma ocean, and indicate that Psyche started as a differentiated
planetesimal and had its mantle stripped, validating the mission’s prime
hypothesis for this body. If the silicates are all primitive chondritic material,
then they were likely added as later impacts, and Psyche may have started life
as a highly reduced metallic body without a significant silicate mantle, or,
the nature of impact flux and its consequences are far more significant than
our current models indicate. The numbers and shapes of craters on Psyche’s
surface may help decipher that story.”The
spacecraft’s gamma-ray and neutron spectrometer (derived from an instrument on the
MESSENGER Mercury orbiter) will help determine the asteroid’s bulk elemental
composition.

Psyche the asteroid won’t be an unchanged relic.Its original surface will have been battered by
numerous impacts over the subsequent billions of years. The hydrated materials recently
discovered on its surface with telescopic studies, for example, are likely to
have been delivered by impacts of other asteroids.It’s possible that by now, the body is a
jumbled rubble pile.The cameras on the
spacecraft (near copies of the cameras that the Mars 2020 rover will carry)
will be tasked with taking the images that will allow geologists to reconstruct
its history.By using filters tuned to
specific wavelengths of visible and near-infrared light, the camera’s images also
will help map the surface’s fine-scale composition.

The planned orbits for the Psyche
spacecraft around its namesake.Credit:
Psyche mission team.

The Psyche asteroid’s sits deep within the asteroid belt at 3.3 times
the Earth’s distance from the sun.(By
comparison Vesta is at 2.6, the asteroid Ceres is at 3, and the Trojan
asteroids average 5.5 times the Earth’s distance from the sun.)To reach this world, the Psyche spacecraft,
like the Dawn spacecraft that has explored Vesta and Ceres, will use solar
electric propulsion to slowly but methodically reach its namesake world.The gentle thrust of its engines will deliver
the spacecraft to Psyche approximately seven years after launch and will allow
it to spiral down to progressively lower orbits.The mission’s planners expect the spacecraft to
orbit as close as 105 kilometers from the surface where the cameras will have a
resolution of 5 meters.

While not yet selected as an approved mission, the NEOCam telescope was
awarded an additional year’s funding to mature its design.For the team proposing this mission, this is
the third time it has vied for selection.It was originally proposed in 2006 and not selected as a finalist and
reproposed in 2010 when it was awarded funding to mature the technology of its
sensors.If the mission eventually is
funded by NASA, it would have two goals.The first would be oriented toward protecting our planet by discovering
a large number of the small (from a few tens of meters across up to a
kilometer), near Earth asteroids that have evaded detection by other means.The second goal would be more scientifically
oriented with the NEOCam telescope expected to also observe more than a million
main belt asteroids and about a thousand new comets.The resulting database would allow sophisticated
analyses on the sizes, compositions, and orbital dynamics of the population of
small worlds.

So far as I can recall, this is the first time that a Discovery mission
finalist has been awarded additional funds to mature its design to be ready for
a future funding opportunity.(Two other
missions from the 2010 competition were also given funding to mature instrument
technologies, but neither were finalists.)NEOCam’s (this is an acronym for Near Earth Object Camera) focus on
small bodies whose orbits lie close to and often cross that of Earth’s places
it at the junction of several of NASA’s programs.From finding and mapping the location of
these objects, there is good science, there is planetary protection, and there
is finding potential worlds for future human exploration or mining.As a result, says NASA’s Green, the additional
funding awarded to mature NEOCam’s design is seen as a strategic investment.

Unfortunately, missions to Venus are not seen as a strategic investment
and both finalists for this planet are simply left as unselected.I was very disappointed to see that neither
was selected.(I had hoped for the selection
of one Venus and one asteroid mission.)I
believe that this world can tell us much about the evolution of terrestrial
planets in our solar system and represents what is likely to be a relatively
common class of larger rocky worlds around other stars.

So for fans of Venus and for all the other solar system destinations,
what are the opportunities for selection of future missions?The European Space Agency is currently reviewing
proposals for its fifth medium class science mission, which would enable
planetary missions roughly the same capability as NASA’s Discovery
program.I know that there is a proposal
for a Venus
mapping mission and a Saturn orbiter to study the moons Titan and
Enceladus.Based on proposals for the
last competition, there are likely to be other missions proposed to study other
solar system bodies including orbiting main belt asteroids.The planetary mission proposals are in
competition not only with each other but also with astrophysics and
heliophysics missions.The selection of
finalists for this competition is expected by June, the selection of the final
winner is expected around 2019 with a launch around 2029.

NASA has just begun the process to select its next New Frontiers
mission, which will have a total budget (likely $1.2 billion or more) 80-100%
larger than the Discovery missions (likely $675 million or more).These missions are selected from a
pre-approved list of high priority missions.For this competition, this list is:

Comet Surface Sample Return

Lunar South Pole-Aitken Basin Sample Return

Titan and/or Enceladus

Saturn Atmospheric Probe

Venus atmospheric probe and lander

Trojan Asteroid Tour and Rendezvous

We don’t know what the selection of the Discovery Lucy mission, which
will study Trojan asteroids, will have on the chances for the selection of a
New Frontiers Trojan mission.The
selection of the finalist proposals is expected in November, the final
selection in mid-2019, and launch by the end of 2025.

Finally, NASA plans – subject to the generosity of the President and
Congress with future funding – to launch Discovery missions approximately every
three years.With the launch for the
Psyche mission in 2023, the 15th mission in this series should launch
around 2026.Working backwards from that
date, we might see the start of the next completion late this decade and selection
of the next mission(s) in the early 2020s.There were many exciting missions proposed for this just completed
competition; many are likely to be re-proposed.And we are likely to see new ideas put forth.

As the selection of Lucy and Psyche shows, these competitions among
scientists result in creative and scientifically rich missions.By the mid-2020’s we should have another two
or more new missions to look forward to.

4 comments:

Always happy when NASA selections a robotic mission, but I have to admit I am at a crossroads with the 2 selections, especially since the next won't be for 3-5 years as you said. Although valuable missions, here are my points.

The selections to me show a clear sign that NASA is taking the Discovery class of missions to heart and going forward will reserve these low cost missions for those unique mission types. With no Venus selection (out of 2), it will defer a return via the New Frontiers selection next year. Now, we do NEED to get back to Venus, but we also need to get back to Titan and Enceladus with a LIFE type of mission and my concern is that this selection just put that in jeopardy.

We know the next Flagship will be the 2 Europa missions and I am ecstatic about that....but we also do need to find a way to get to these 2 moons ASAP. It will require an RTG so the New Frontier program is the only option, but again, it may not be for some time.

Perhaps on your next post you can provide your insight/analysis on what this Discovery selection means going forward. Thanks again and as always, look forward to your work.

The Trojans were a strong contender for New Frontiers (Trojan Tour and Rendezvous), but now that Lucy has been approved, what aspects of the Decadal Survey have not been covered? Obviously the 'tour part' covers a major part, does this mean that a 'rendezvous' with for instance Hektar could be undertaken by another Discovery mission, thereby completing the full Decadal Survey requirements?

Has any more been said about possible destinations for the Lucy extend mission?Also if Psyche was to have its own extended mission, are its scientific instruments of limited use on other nearby asteroids etc?

@Ken - The Europa lander mission is approved. I'm hearing rumblings that it may be very expensive... We will also see what the next Decadal Survey has to say.

@Edmund - A future mission could do a rendezvous with one or more Trojan asteroids. I know of at least one team that planned to propose a mission to the New Frontiers competition. Other nations could also do a mission.

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.